Disturbances of sleep are extremely common in the general population. Because of the large number of people seeking treatment for these disturbances, we opened a sleep clinic at the University of Cincinnati, primarily for the diagnosis and treatment of these disorders. 1 A secondary function of the clinic was to help us gain information that would enhance our understanding of the various sleep disorders and permit us to evaluate the different treatment modalities for the different sleep disorders. The most common complaint of people seeking treatment at the clinic was insomnia. The present report is an attempt to provide a summary of some of our observations about the nature of insomnia. The data base for the present report consists of the information we gathered on the first 54 insomniac patients we saw at the Sleep Clinic. The data will be presented under several categories: demographic information, nature of sleep complaint, sleep laboratory observations, psychological testing, general health, and the subjective evaluation of sleep.